A defense lawyer dropped a courtroom bombshell yesterday – accusing a hit man of accepting a $50,000 offer from his would-be victim to turn informant and help crack a sensational murder-for-hire case.

That’s twice as much as he was offered for the hit itself.

The informant – whose name is being kept confidential – was offered the money by the alleged target, Robert Jacobs, said defense lawyer Ben Brafman. He predicted the star prosecution witness is now so “tainted” that the case will “self-destruct.”

Jacobs, a Bergen County, N.J., businessman, “agreed to pay $50,000 of his own money to the informant to make his case before the government,” Brafman said during a pretrial hearing.

Brafman declined to comment on prosecutors’ role, if any, in the payment – less than half of which he said was actually given to the informant in return for his wearing a wire and promising to testify.

It was not clear how Jacobs learned the identity of the hit man or contacted him to make the offer.

Brafman’s client, lower Manhattan jeweler David Sabo, is the alleged middleman in what prosecutors have called a “murder conspiracy” involving tens of millions of dollars in real estate.

In court papers, Jacobs blames three business adversaries, with whom he is embroiled in numerous lawsuits, for setting up the hit through Sabo.

Sabo – the only one charged – faces up to life in prison. He’s charged with attempted murder for allegedly hiring the informant to bump off Jacobs.

Prosecutors photographed Jacobs posing “dead” with a fake bullet wound in an attempt to catch Sabo paying the balance on the $25,000 hit. But Sabo was busted after allegedly incriminating himself by demanding further proof that the hit had happened.